The problem for providing adequate protection for valuable equipment that is necessarily stored in truck trailers at construction sites has existed for many years. Numerous devices have been designed and used with and without some success. One such device is in U.S. Pat. No. 3,736,016 wherein a cover is provided and the padlock is inside the cover. Another similar device is in U.S. Pat. No. 4,300,369. While these devices do provide some protection, they use only the normal connections of the locking device to the rear doors of the trailer. U.S. Pat. Nos. 3,656,788, 3,809,417 and 4,078,836 disclose means for locking doors which employ some type of telescoping members. However, the locking means disclosed in these patents would not be readily adaptable to be mounted on the outside surface of the rear doors of a truck trailer. U.S. Pat. No. 3,820,662 discloses a locking means for a bicycle wherein a cable is secured at one end in a tube so as to resist any attempt to saw completely through the tube.